Asymmetrical trigger circuit



INVENTOR A. H. DICKINSON ASYMMETRICAL TRIGGER CIRCUIT Filed Jan. 12, 1949 vvvvv May 1, 1951 Jo WM 3 Patented May 1, 1951 ASYMMETRICAL TRIGGER CIRCUIT Arthur H. Dickinson, Greenwich, Conn., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application January 12, 1949, Serial No. 70,495

2 Claims.

This invention relates to trigger circuits employing two grid controlled tubes switchable to either of two stable conditions alternately and more particularly to such a trigger circuit which is asymmetrical;

In trigger circuits having two stable conditions and employing two grid controlled tubes, it is conventional to comiect the plate of each to the control grid of the other through symmetrical portions of symmetrical fixed impedance networks. In such circuits the control grids of the tubes are frequently connected to a common source of pulses and the trigger switched from each stable condition by the application of the pulses simultaneously to the control grids of the two tubes.

One of the objects of this invention is to provide additional electron tubes, intermediate the control grids of the electrontubes of the trigger and the common source of pulses, for switching the trigger by supplying simultaneously, separate pulses to said control grids from the common source of pulses.

- Another object is to provide an electrical circuit for providing from a common source of pulses two series of pulses, each independent of the amplitude of the other, to the control grids of the respective tubes of a trigger circuit.

Still another object is to provide an asymmetrical trigger circuit having two stable conditions and switchable from either condition to the other in response to pulses from a common source of pulses.

A further object is to provide a trigger circuit having two similar grid controlled tubes with the plate of each connected to the control grid of the other, the potential applied to the electrodesof each tube being of a different value from that applied to the corresponding electrode of the other tube.

A still further object is to provide a dual tube trigger circuit having two stable conditions alternately assumed, the control grid bias of one tube being determined by the plate Voltage of the other.

Another object is to provide a dual-tube trigger circuit having two stable conditions alternately assumed wherein only one fixed impedance network is employed.

Still another object is to provide a trigger circuit switchable to one stable condition in response to an increased impedance in a variable impedance network and switchable to the other stable condition in response to an increased impedance in a variable impedance.

A further object is to provide an improved trigger circuit of the grid controlled dual-tube type arranged asymmetrically and switchable to either of two stable conditions alternately in response to pulses applied to the control grids of the grid controlled tubes.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawing, which discloses, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

The drawing is a circuit diagram illustrating the principles of the invention.

Referring more particularly to the drawing, an input terminal I0 is connected by a conductor l l and a capacitor it! of 0.00005 microfarad to the cathodes of diodes l3 and I4 which are of the 6H6 type. These cathodes areconnected through a resistor l5 of 100,000 ohms to a zero volt line l6. The plates of the diodes l3 and M are connected through resistors I1 and I8, respectively, each of 100,000 ohms to a plus volt line I 9.

Triodes Z0 and 2| together comprise one 6SN7 dual-type tube and are connected to form the trigger circuit of the invention. The cathodes of triodes 20 and 2| are connected respectively to the plus 90 volt line I 9 and a plus volt line 22 and the plates to a plus 240 volt line 23 through a resistor 24 of 100,000 ohms and a resistor 25 of 45,000 ohms, respectively.

The plate of triode 20 is also connected, through a conductor 26 and parallel connected potentiometer 21 and capacitor 28 of 0.00005 microfarad to the control grid of triode 2!. The plate of triode 2| is connected through a conductor 29 and parallel connected resistor 30 of 400,000 ohms and capacitor 3| of 0.00015 microfarad to the control grid of triode 20. A bias resistor 32 of 270,000 ohms is connected between the control grid of the tube 20 and the zero volt line I6.

The plate of the diode I3 is also connected, through a conductor 33, a capacitor 34 of 0.00005 microfarad, a potentiometer 35 and a conductor 35' to the control grid of the triode 2 l. The plate 3 of the diode I4 is also connected, through a conductor 31, a capacitor 38 of 0.00005 microfarad, a potentiometer 39 and a conductor to the control grid of the triode 20.

The diodes |3 and I4 and associated circuit serve to supply simultaneous but separate pulses to the control grids of the triodes 20 and 2|, from a common source connected to input terminal l supplied with a series of negative pulses. When a source of negative pulses is applied to the terminal I0, they are transferred through the conductor II and capacitor l2 to the cathodes of the diodes l3 and It to render their cathodes sufficiently negative to cause conduction therethrough. As a result, the voltage at the plates of diodes l3 and 14 decreases. This decrease or negative pulse at the plate of diode i3 is transferred through the conductor 33, capacitor 34, potentiometer 35 and conductor 30, to the control grid of triode 2| while the negative pulse at the plate of diode M is transferred through the conductor 31, capacitor 38, and potentiometer 39 to the control grid of triode 20. n t

It is apparent that the amplitude, duration and repeat frequency of the pulses, applied to the terminal I0, may vary withinwide limits. But, it is essential that the pulse amplitude be large enough to cause sufficient conduction through diodes l3 and M to produce, at their plates, negative pulses having sufiicient amplitude to effect a switching of triodes 2E! and 2|, from the conductive to the non-conductive condition.

Potentiometer arms 35a and 39a respectively associated with the potentiometers 35 and 39 are provided to adjust the amplitude of the negative pulses applied to the control grids of triodes 20 and 2| for optimum trigger operation. However; it will be understood that the adjustment of pulse amplitude is not essential to a practice of the invention, the only requirement being that the negative pulses, applied to the control grids of triodes 20 and 2|, be of sufficient amplitude to effect a switching of these triodes'from the conductive to the non-conductive condition.

For purposes of explanation the trigger is assumed .to be in the off condition at starting in which condition triode 20 conducts and triode 2| is non-conducting. The dot at the lower right-hand side of triode 20 indicates that it is conducting and thus that the trigger is off. When triode 20 becomes non-conductive and triode 2| conductive, the trigger is referred to as being on.

When the first negative pulse is applied to the input terminal It, a negative pulse is thereupon transferred over the conductor 35 to the control grid of the non-conductive triode 2| but is ineffective as it merely tends to make this control grid still more negative. Simultaneously, a negative pulse is transferred from the plate of the diode [3 through the potentiometer 39 to the control grid of the conductive triode 2|! and drives its control grid bias toward the cut off value. As a result of the decreased conduction of triode 20, its plate becomes more positive and the positive pulse thus formed is transferred over conductor 26 and the parallel connected potentiometer 21 and capacitor 28 to the control grid of triode 2|. This renders its control grid sufiiciently positive to start conduction therethrough. When this conduction occurs, its plate becomes less positive and the negative pulse, thus formed, is transferred over conductor 29, andthey parallel connected resistor 30 and capacitor 3| to the control grid of triode 20, to render that grid, still more negative, to thus decrease the conduction therethrough still more. Again the positive pulse formed at its plate is transferred to the control grid of triode 2| to cause it to become more conductive. The resulting negative pulse formed at the plate of the triode 2| is transferred to the control grid of triode 20 to render it less conductive. This cumulative action continues until triode 20 becomes nonconductive and 2| becomes fully conductive thereby placing the trigger in the on condition.

When the second negative pulse is applied to the terminal ID, the negative pulse thereupon applied to the control grid of the non-conductive triode 20 is'ineifective to render it conductive. However, the negative pulse applied over conductor 36 to the control grid of the conductive triode 2| renders it less conductive. The resulting positive pulse at the plate of triode 2| is transferred over conductor 29 and the parallel connected resistor 30 and capacitor 3| to the control grid of triode 20 thereby rendering it conductive, The resulting negative pulse at its plate'is transferred over conductor 23 and the parallel connected potentiometer 21 and capacitor 23 to the control grid of triode 2| to render it less conductive. Again, the positive pulse formed at its plate is transferred over conductor 29 and the parallel connected resistor 30 and capacitor 3| to the control grid of triode 20 to render it more conductive. The resulting negative pulse at its plate is transferred to the control grid of triode 2| to render it still less conductive. This cumulative action is continued, until the trigger is returned to the starting or off condition, in which triode 20 is conductive and triode 2| non-conductive as illustrated.

In the same manner, succeeding negative pulses applied to the terminal l0 cause the trigger to switch on and off alternately.

It is seen from the above explanation that when the impedance of the conducting triode of the trigger changes as exhibited by a decrease in its conduction, the resulting increased voltage at its plate is transferred over the parallel connected resistor and capacitor to the control grid. of the non-conducting triode to render it conductive. The network consisting of the resistors 25, 30 and 32 and the capacitor 3! is a fixed impedance network. Such a fixed impedance network is conventional in such triggers, the resistor 25 serving as a plate load, the resistor 30 and the capacitor 3| coupling the plate of one tube and the control grid of the other and the resistor 32 serving to place the proper bias on the control grid of one tube. In the conventional trigger, a similar fixed impedance network is associated with each grid controlled tube to provide a symmetrical circuit for assuring the alternate switching of the trigger to the two conditions of stability. Also, like voltages are applied to the corresponding electrodes of the grid controlled tubes of the trigger. The novel trigger of this invention however is not dependent on either of these conditions and effects a saving of circuit components. This novel trigger is asymmetrical and is switched to its stable conditions in a novel manner.

In the conventional trigger, the resistor 24, potentiometer 2!, capacitor 23 and a resistor between the control grid of triode 2! and the zero volt line I6 would comprise a second fixed impedance network for performing functions simir the tubes.

lar to those performed by the fixed impedance network of triode 20. In this novel trigger," no connection is required between the control grid of triode 2i and the zero volt line and, as explained hereinafter, potentiometer 21' .may be eliminated and the control grid of triode 2| con nected conductively to the plate of triode 20 thereby eliminating both the potentiometer 2'! and the capacitor 28.

- Whether potentiometer 21 and capacitor 23 be used or not does not change the principle of operation, since in either event the only bias supplied to the control grid of triode 2! is the Zoltage transferred to it from the plate of triode A resistor and a capacitor between the plate of each triode of the trigger and the control grid of the other are ordinarily provided to limit the objectionable effects of the interelectrode capacity of the tubes. In choosing this resistor and capacitor for use in a trigger to be operated over a wide range of repeat frequencies, it is difiicult to obtain such values as will effectively limit or neutralize the interelectrode capacity of the tubes and not cause objectionable exponential variations in the voltages and currents produced by Because of these operational difficulties, the potentiometer 2i and the capacitor 28 are provided to be adjusted or eliminated entirely as found necessary to obtain optimum operation of the trigger.

In addition to the use of only one fixed impedance network and one bias resistor, the asymc metry of the trigger circuit is further accentuated by the difference in the values of the load resistors 24 and 25 and the different voltages applied to the cathodes of the tubes. The load resistor 24 has a value of 100,000 ohms and 90 volts are applied to the cathode of triode 20 while the load resistor 25 has a value of only 45,000 ohms and 165 volts are applied to the cathode of the tube 2 i.

For the purpose of explaining more clearly the operation peculiar to my trigger, the resistors25, 30 and 32 with the capacitor 3|, will be referred to as the fixed impedance network, triode 20 and the resistor 24 as the variable impedance network, and triode 2! as the variable impedance. Since the potentiometer 21 and the capacitor 28 are not essential to the invention, reference thereto will be omitted in the subsequent explanation and a simple conductor will be assumed as substituted therefor between the plate of triode 20 and the control grid of triode 2|.

Now, when the first negative pulse is applied to the control grids of triodes 20 and 2 I, the increase in the impedance of the variable impedance network causes a transfer of a positive pulse over conductor 28 to the variable impedance, to institute the switching of the trigger. The resulting decrease in value of this variable impedance causes a transfer of a negative pulse over the fixed impedance network to the control grid of triode 2% to increase further the impedance of the variable impedance network. This action is continued until the trigger is switched on. Hence, as the trigger is switched on, an increase in the variable impedance network controls the variable impedance to decrease its value and the variable impedance utilizes the fixed impedance network to increase further, the value of the variable impedance network.

When the second negative pulse is applied to the control grids of triodes 20 and 2|, the increase in the variable impedance causes a transfer of a positive pulse through the fixed impedance network to decrease the impedance of the variable impedance network. This decrease causes a transfer of a negative pulse to the vari,- able impedance to increase further its impedance. This action is continued until the trigger is switched off. Hence, as the trigger is switched .Qoff, an increase in the impedance of the variable impedance, controls through the fixed impedance network, the impedance of the variable impedance network which further increases the value of variable impedance.

While .there have been shown and described and pointed out the fundamental .novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A circuit comprising a pair of diodes having a common cathode connection and conductive in response to a source of pulses applied thereto, a plate load resistor for each diode, a trigger circuit having first and second grid controlled tubes and on and ofi conditions of stability, a single fixed impedance network coupling the plate of the first grid controlled tube to the control grid of the second grid controlled tube; a potentiometer and capacitor connected in parallel between the plate of the second grid controlled tube and the control grid of the first grid controlled tube, a capacitor and potentiometer connected in series between the plate of one diode and the control grid of the first tube for transferring a negative pulse to the control grid of the first tube to lessen conduction therethrough, and a capacitor and potentiometer connected in series between the plate of the other diode and the control grid of the second tube for transferring a negative pulse to the control grid of the second tube to lessen conduction therethrough.

2. An asymmetrical trigger circuit comprising first and second grid control tubes having two conditions of stability alternately assumed; a plate load for each of said tubes; a fixed impedance network including the plate load of the second tube, a parallel connected resistor and capacitor joining the plate of the second tube to the control grid of the first tube and a bias resistor for the control grid of the first tube; a potentiometer and a capacitor connected in parallel from the plate of the first tube to the control grid of the second tube, the only bias voltage on the control grid of the second tube being that transferred from the plate of the first tube, said potentiometer enabling adjustment of said trigger circuit for optimum operation; a pair of diodes arranged to be normally non-conducting and having a common cathode connection so that said diodes are rendered simultaneously conductive in response to negative pulses applied to said common connection; a capacitor and a potentiometer connected in series between the plate of one diode and the control grid of the first tube for transferring a negative pulse to the control grid of the first tube to lessen conduction therethrough and a capacitor and potentiometer connected in series between the plate of the other diode and the control grid of the second tube for 7 8 transferring a negative pulse to the control grid Number Name Date of the second tube to lessen conduction there- 2,447,800 Dickinson Aug. 24, 1948 through. 2,459,723 Schantz Jan. 18, 1949 ARTHUR; H. DICKINSON. 2,459,852 Summerhayes Jan. 25, 1949 6 2,467,777 Rajchman et a] Apr. 19, 1949 REFERENCES CITED 2,478,683 Bliss Aug. 9, 1949 The following references are of record in the OTHER REFERENCES file of thls patent Electronic Industries, July 1945, Present In- UNITED STATES PA'I'ENTS 1o terval Timer, pages 97-99, 130, 134, 138, 142, 146. Number Name Date Time Bases, October 1943, by Puckle, John 2,422,204 Meacham June 1'1, 1947 Wiley and 8 4 p 2,441,006 Canfora May 4, 1948 

